A stronghold is a building, fortress, castle, lighthouse or any other super strong constructed structure that is totally safe from any kind of external enemy attack. A fort is a picture perfect example of a stronghold. Also a castle or fort surrounded by stone walls and moats is another kind of stronghold; Most of the strongholds are are built to keep the people, property, productive resources and valuables inside them safe from invading armies and plundering enemies.
A Stronghold can be of Elohim Yahweh and that of Satan the adversary too.
A spiritual stronghold is a scriptural and strong pattern of thought, built into one's mindset, thus having resilient beliefs and convictions. Satan and his workers want to capture the minds of people: the mind is the stronghold of the soul. He who controls the mind controls a very strategic place!